The drop down menu for this should be a pop up menu, since as soon as there is any subtantial content to a post, the options are not visible on screen.
This is how it looks with no content, when you can easily make a choice:
As a temporary workaround, try zooming out a bit. Ctrl + mousewheel. This’ll shrink the interface down so you can access those menu options until this gets fixed.
I mostly have a similar issue with the creator page, when editing or writing the “about” text, the tool bar for editing the text stays at the top and makes it super impractical to edit anything longer down.
I have this issue, too. It seems to be worse in Firefox.
Please make those menus pop-up rather than drop-down, or find a way to make the window drop down while clicking on that button.